Fire broke out late Thursday afternoon at J.J. Auto Masters on Main Street, New Milford.
According to reports, the shop was closed at the time of the blaze, which started in the back of the building. The roof of the structure collapsed. No injuries were reported.
Route 11 was closed for several hours while firefighters brought the flames under control.
The fire marshal was expected to be at the scene on Friday to help determine the cause of the blaze.
It was the second large structure fire in New Milford for Columbia Hose Company, last week.
On Tuesday, July 17, a home, located on Montrose Street, sustained significant damage.
The fire was reported by neighbors at about 12:30 a.m. The home was vacant at the time of the blaze, according to reports.
That fire was believed to be suspicious, and anyone with information is asked to call the Troop R Fire Marshal Unit, (570) 963-3156.